1. Field of the Invention
The present invention relates to cationic electrodeposition and, more particularly, relates to resinous electrodepositable compositions which deposit on the cathode.
2. Brief Description of the Prior Art
Electrodeposition as a coating application method involves the deposition of a film-forming material under the influence of an applied electrical potential, and has become of increasing commercial importance. Along with the increased use of such methods has been the development of various compositions which provide more or less satisfactory coatings when applied in this manner. However, most conventional coating techniques do not produce commercially usable coatings, and electrodeposition of many coating materials, even when otherwise successful, is often attended by various disadvantages such as non-uniform coatings and by poor throwpower, that is, the ability to coat areas of the electrode which are remote or shielded from the other electrode. In addition, the coatings obtained are, in many instances, deficient in certain properties essential for their utilization in certain applications for which electrodeposition is otherwise suited. In particular, properties such as corrosion resistance and alkali resistance are difficult to achieve with the resins conventionally employed in the electrodeposition process, and many electrodeposited coatings are subject to discoloration or staining because of chemical changes associated with electrolytic phenomena at the electrodes and with the types of resinous materials ordinarily utilized. This is especially true with the conventional resin vehicles used in electrodeposition processes which contain polycarboxylic acid resins neutralized with a base; these deposit on the anode and because of their acidic nature, tend to be sensitive to common types of corrosive attack, for example, by salt, alkali, and so forth. Further, anionic deposition tends to take place with the uncured coating in proximity to metal ions evolved at the anode, thereby causing staining of many coating systems.